The present invention relates generally to apparatus and methods for mixing cementitious materials, such as mortar and grout, and more particularly relates to portable systems for mixing these materials at construction sites.
Disclosed in copending U.S. application Ser. No. 252,379 is a portable, on-site system for batch mixing cementitious construction materials, such as mortar and grout, which has proven to be a substantial improvement over prior on-site batch mixing systems. The system includes a truck-transportable batch mixing machine operative to store and batch-mix the three components of cementitious construction material-namely, cement, sand and water. The machine supports, on a frame structure, water, cement and sand storage and dispensing vessels which, via a mixing control system described in detail in the copending application, accurately deliver predetermined quantities of these three stored constituents to a bladed batch mixer portion of the machine used to subsequently mix a desired "batch" of the resulting grout, mortar or the like for construction site use.
The relatively small truck used to deliver the batch mixing machine to the job site is also used to shuttle four cement transport containers back and forth between the mixing machine (and other mixing machines previously delivered to the job site) and a main cement storage area at the site. Each portable cement container is sized to hold a quantity of cement generally equal to that of the cement reservoir of the mixing machine into which the hopper load is dumped when necessary.
The water level in each mixing machine's water storage tank is float controlled, with the tank being elevated with respect to the batch mixer into which tank water is periodically gravity-delivered via an outlet pipe interconnected between the elevated water storage tank and the mixer.
The cement reservoir on each machine is internally provided with a rotating cement "conditioner" structure designed to maintain the stored cement therein in a condition facilitating the generally uniform outflow of stored cement from its storage reservoir into the mixer upon demand.
A large supply of sand is typically dumped on the ground adjacent each mixing machine and, as needed, portions of this large pile are scooped up into the machine's sand reservoir inlet using a front end bucket loader.
While this batch mixing system briefly described above has proven to provide substantial benefits and advantages, especially when servicing job sites with smaller volume requirements, its use has demonstrated that even further improvements therein would be desirable from economic, operational and maintenance standpoints.
Substantial economics of operation at job sites requiring greater numbers of batch volumes can be effected using in combination with the system a bulk cement storage facility which automatically delivers cement to the batch cement mixing proportioning hopper. This not only allows the cement to be purchased in truckload lots but reduces equipment and manpower costs because the use of the machine transport truck as a cement container shuttle vehicle necessarily entails additional manpower costs as does the necessity for worker handling of the relatively small containers as they are unloaded from the truck, placed atop the mixing machine, emptied into the machine's cement reservoir, and then placed back onto the truck to be shuttled back to the main cement storage area. In addition to the increased manpower costs inherent in this container shuttle procedure, a transport truck breakdown can significantly delay the overall batch mixing process. To avoid such delay, it is common practice to keep a standby truck readily available, thereby further increasing the overall cost of batch mixing cementitious materials at the construction site.
The float control system for the mixing machine water storage reservoir, while of a simple and normally quite reliable construction, is, as many float control structures are, prone to corrode, stick, and generally "gum up" with advancing age, thereby necessitating periodic replacement with its attendant cost and downtime. Moreover, when the water reservoir tank is provided with an optional water heating system, the temperature of the water in the tank tends to vertically stratify which undesirably causes variances in the temperature of water delivered to the batch mixer.
The conditioning of the cement within its machine storage and dispensing reservoir is, as was generally described above, carried out via a motor-driven rotating arm structure within the reservoir. The operation of the rotating arm structure is designed to facilitate and augment the cement conditioning or "fluffing" action of pressurized air injected into the bottom of the machine's cement reservoir. In use of the machine it has been found that some cement metering inconsistencies still exist due to the fact that the injected air tends to form within the reservoir, along essentially the entire height of the stored cement, a central vertical column of aerated cement.
This vertical column of aerated or "fluffed" cement has essentially the same effect as a liquid column that creates a pressure at its bottom which varies directly with the height of the column. Accordingly, the conditioned cement discharge rate tends to vary with the quantity of cement in the reservoir at a given time. Additionally, the rotating arm structure requires a relatively large drive motor and various related controls, and is subject to abrasion and wear from the stored cement through which it is rotated.
The batch mixer portion of the overall cementitious material mixing machine illustrated in copending U.S. application Ser. No. 252,379 is provided with a generally conventional bearing and seal structure operatively associated with the drive shaft which extends through the mixer housing. In common with the shaft bearing/seal structures on other types of cementitious mixers, it has been found that this structure requires frequent greasing maintenance, and tends to rather quickly permit seal abrasion and resulting entry of the cementitious mixture into the shaft bearing. Such entry of the abrasive mixture into the shaft bearing, as is well known, leads to premature bearing failure.
The conventional piling of a large sand supply on the ground adjacent the mixing machine carries with it the potential problem of contaminating the cementitious mixture with earth unintentionally scooped up with sand by the front end bucket loader.
In view of the foregoing, it is accordingly an object of the present invention to provide, in the areas set forth above, improvements to the portable, on-site cementitious construction material mixing system illustrated and described in copending U.S. application Ser. No. 252,379 incorporated herein by reference.